Properties of Molecular-Based Frustrated Magnets

Wynn, Charles M.; Albrecht, A. S.; Landee, Christopher P.; Navas, C.

doi:10.1080/10587259508031859

Cited by 8 publications

(1 citation statement)

References 14 publications

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“…We reported two types of cobaltous tricarboxylate compounds: one is a series of molecular cavities constructed from aromatic BTC (BTC = 1,3,5-benzenetricarboxylate), and the other is a coordination polymer of nonaromatic CTC (CTC = 1,3,5-cyclohexanetricarboxylate). , For BTC, none of the networks to have been characterized structurally have been shown to display long-range magnetic ordering. There is only one example that exhibits long-range ordering, but its structure is not reported . On the other hand, CTC generates open-framework structures with sizable channels and behaves as short-range coupled low-dimensional chains with a tendency for ferrimagnetic alignment .…”

Section: Introductionmentioning

confidence: 99%

Construction of Hydrogen-Bonded and Coordination-Bonded Networks of Cobalt(II) with Pyromellitate: Synthesis, Structures, and Magnetic Properties

2002

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Synthesis (hydrothermal and metathesis), characterization (UV-vis, IR, TG/DTA), single-crystal X-ray structures, and magnetic properties of three cobalt(II)-pyromellitate complexes, purple [Co(2)(pm)](n) (1), red [Co(2)(pm)(H(2)O)(4)](n) x 2nH(2)O (2), and pink [Co(H(2)O)(6)](H(2)pm) (3) (H(4)pm = pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid)), are described. 1 consists of one-dimensional chains of edge-sharing CoO(6) octahedra that are connected into layers via O-C-O bridges. The layers are held together by the pyromellitate (pm(4-)) backbone to give a three-dimensional structure, each ligand participating in an unprecedented 12 coordination bonds (Co-O) to 10 cobalt atoms. 2 consists of a three-dimensional coordination network possessing cavities in which unbound water molecules reside. This highly symmetric network comprises eight coordinate bonds (Co-O) between oxygen atoms of pm(4-) to six trans-Co(H(2)O)(2). 3 possesses a hydrogen-bonded sandwich structure associating layers of [Co(H(2)O)(6)](2+) and planar H(2)pm(2-). The IR spectra, reflecting the different coordination modes and charges of the pyromellitate, are presented and discussed. The magnetic properties of 1 indicate complex behavior with three ground states (collinear and canted antiferromagnetism and field-induced ferromagnetism). Above the Néel temperature (T(N)) of 16 K it displays paramagnetism with short-range ferromagnetic interactions (Theta = +16.4 K, mu(eff) = 4.90 mu(B) per Co). Below T(N) a weak spontaneous magnetization is observed at 12.8 K in low applied fields (H < 100 Oe). At higher fields (H > 1000 Oe) metamagnetic behavior is observed. Two types of hysteresis loops are observed; one centered about zero field and the second about the metamagnetic critical field. The critical field and the hysteresis width increase as the temperature is lowered. The heat capacity data suggest that 1 has a 2D or 3D magnetic lattice, and the derived magnetic entropy data confirm an anisotropic s(eff) = 1/2 for the cobalt(II) ion. Magnetic susceptibility data indicate that 2 and 3 are paramagnets.

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